1. Field of the Invention
The invention relates to an arrangement for monitoring and controlling webs of packaging material or the like in respect of material and positional defects, especially on packaging machines, with sensors, preferably photoelectric transmitters and receivers, for sensing the continuous web.
2. Description of Related Art
In connection with packaging machines, it is necessary to monitor webs of material, especially webs of packaging material. On the one hand, it is important to identify material defects, for example holes and tears, but also web joins made by adhesive tape, etc. When defects of this type are detected, one or more packs, especially cigarette packs, produced from the packaging material having these defects are separated out. However, it is also necessary, furthermore, to monitor the run of the web of material, that is to say its relative position. When there are deviations from the desired positions, the sheet is adjusted into the correct direction of movement by suitable adjusting members.
A monitoring and control arrangement of this type is described in EP-A-25,563. In this known proposal, a reel carrier has assigned to it a photoelectric sensing device which consists of two sensor bars arranged at a distance from one another. The web of packaging material runs through between these in such way that a row of sensors arranged at a slight distance from one another extends on each of the two sides of the web. Furthermore, there are on each sensor bar two lateral sensors (transmitter and receiver) which sense the side edges of the sheet and which detect any skewing. In the known device, these last-mentioned sensors or any error signals are used to actuate a servo-motor which correctly adjusts the reel or reel mounting.
Although the known arrangement is suitable for monitoring material and positional defects in a web of material, nevertheless it involves a relatively high outlay in terms of construction and handling.